Self-service gasoline stations have become widely popular in recent years as a lower cost means of dispensing gasoline. Self-service stations require less personnel, thereby cutting down on the operating costs for the station owner, resulting in greater profits, and savings which can be passed on to customers in the form of lower fuel prices. While there are many advantages to these stations, there are also several problems which can arise. One problem which occurs infrequently, but which can have serious consequences, is when a customer forgets to remove the fuel nozzle from a vehicle's fuel tank inlet before driving away. This situation, which is known as a "drive away", can be very hazardous and costly. When a drive away occurs, a tremendous force is created on the fuel hose attaching the nozzle to the fuel dispenser. This force can cause the hose to rupture, spilling fuel all about the station and creating a serious fire hazard. In addition, the force on the hose can travel back to the dispenser and cause the dispenser to be ripped out of its base or pedestal, or damaged in a variety of other ways. This results in the need for expensive repair work or replacement of the dispenser. Therefore, it has been desirable to find a coupling device which will enable a fuel nozzle to disengage from a dispenser without damage or fuel spillage.
In the past, breakaway units have been developed which enable a fuel hose to be easily and safely severed in the event of a drive away. Among the approaches that have been developed are breakaway units which comprise a valve in series flow relation with a fuel hose and a fuel nozzle. In these units, the tension force caused by the drive away is exerted on the hose, separating or disconnecting the breakaway valve when that force exceeds a force which would cause the hose to rupture, or otherwise cause damage to the dispenser and spillage of fuel which would create a fire hazard. These units typically include valves of the so-called "dry disconnect" type which seal the separated portions of the valve so that there is only a minimal amount of fuel released when a drive away occurs.
Recently, service stations have begun using so-called "high hose" dispensers in which the nozzle hose is connected to and extends from the upper portion of the dispenser. This type of dispenser is typically anchored at its base on a pedestal, or island, at a service station. This places the point of connection of the fuel hose some eight to twelve feet above ground level. Thus, when a drive away occurs, the pull of the hose on the dispenser has a high leverage tending to topple the dispenser. This has led to a requirement that the maximum permissible breakaway force be set at lower levels than were previously accepted as providing adequate protection.
The reduction of the force required to separate a hose breakaway unit introduces a further problem in that the lowered, permissible, breakaway force approaches the hydraulic, line shock forces which can be generated in a hose when the nozzle valve suddenly closes. Many nozzles have a mechanism for automatically closing the nozzle valve when the fuel in a vehicle's tank reaches a predetermined level. Many such mechanisms close the nozzle valve substantially instantaneously, while fuel is being delivered at a high flow rate. Such closure can result in momentary line shock forces on the hose which can be considerably higher than the desired maximum breakaway force of 250 pounds. Thus, close tolerances must be maintained in the breakaway force of the coupler to prevent decoupling during normal operation.
The most widely used hose breakaway units depend on shear pins (or other elements which fracture) as the means to release a delivery hose in the event of a drive away. Shear pins have long been recognized as a reliable means for decoupling one element from another when a load exceeds a given limit. However, where they are subject to repeated loads approaching their failure strength, as would be generated by line shock forces, fatigue stresses reduce the force at which shear occurs. Breakaway valves embodying shear pins thus become unreliable in that they can separate, to render a nozzle unserviceable, in the normal delivery of fuel. This is both an inconvenience as well as an undesirable expense to the fuel vendor.
Thus, even though shear pins can initially provide a close tolerance in the force at which they will fail, fatigue stresses can increase this tolerance so that failure occurs at a force much lower than required for practical, safety purposes.
Other hose breakaway units have been developed which do not depend on shear pins to separate the unit in the event of a driveway. These units typical utilize a resilient member such as a spring to maintain the components of the unit in an assembled relation and prevent the unit from easily separating during normal use. Since these units utilize resilient members rather than shear pins to couple the unit, these units can often be reassembled after a drive away separation without the need to repair or replace parts in the unit.
Although the use of springs is beneficial in that it allows the unit to be easily reassembled, springs alone typically do not enable close tolerancing of the separation force. Thus, as the range between the required separation force and the peak line shock forces narrows, it becomes increasingly likely that these units will untimely or prematurely separate. In addition, these breakaway units typically are not able to absorb or dissipate the line shock forces applied to the unit. Without a means to check these forces, additional wear and stress is placed upon the unit, increasing the likelihood that repair or early replacement will be required.
Thus, a need exists for a breakaway unit which has an improved separation force tolerance and which absorbs line shock forces to prevent untimely separation and wear and tear on the unit.